1. Field of the Invention
The present invention is directed to improvements for hand-tools including an hydraulic jack mechanism to control the working members of the hand-tool.
In particular, the present invention relates to tools in which pressure must be exerted on a working member, mounted in a moveable manner in a head, by a hydraulic jack activated by a suction and discharge pump conventionally, controlled manually.
2. Discussion of Background and Material Information
Conventional hand-tools equipped with hydraulic jack mechanisms are typically pincer-type devices normally used to perform operations such as bending, cutting, boring, encasing, and the like. In such devices, the hydraulic jack serves to control the displacement of a moveable jaw, with respect to another fixed jaw, both mounted in a head. Often, these tools are transformable i.e., the jaws-carrying head is interchangeable and fixed to the end of the jack from which the shaft of the piston of the jack emerges in such a manner as to permit one to adapt the type and size of the jaws to the work. Likewise, a given head can be adapted to receive jaws of various shapes and sizes.
U.S. Pat. No. 4,149,381 is a representative example of tools of the previously discussed type.
The pressures to be exerted on the working members, i.e., the tightening ability in the case of pincers, are always great and the hydraulic jack must develop relatively high pressures, on the order of 700 bars and often more.
In almost all cases, the work to be accomplished by means of the tool is a repetitive process which must be effected in a rapid cadence for economic reasons. It is therefore, necessary to reduce, as much as possible, the number of piston thrusts of the pump, required for the total advancement of the piston. For a determined total advancement this number is proportional to the relation D.sup.2 /d.sup.2 in which D is the diameter of the piston of the jack and d is that of the piston of the pump. However, the force to be exerted by the operator, which should not exceed 100 newtons approximately since the tool must be capable of being handled with one hand, is proportional to the reverse relation d.sup.2 /D.sup.2. Of course, the effort required from the operator is also inversely proportional to the arm of the lever of the pump, but there again, one must bear in mind a contrary obligation. The course of the end of the manipulation handle is limited due to the need for manipulation with one hand, for example of approximately 80 millimeters and the arm of the lever cannot be increased except by reducing the stroke of the piston of the pump, whereas the number of thrusts of the piston is clearly inversely proportional to this course.
Until now, with the exception of the particular dispositions adapted to reduce the range of advancement to be carried out by an hydraulic process, i.e., a rapid mechanical approach of the jaws of the pincer, with locking, before advancement under pressure, or other specific means, it was necessary to be satisfied with a compromise permitting acceptable values for each of the parameters (for example: manual effort 130N, number of thrusts of the pump 24, weight of the tool 1.5 kilograms), without allowing the whole to result in optimum conditions of performance and comfort.